1. Field of the Invention
The present invention relates generally to computer systems, and more particularly, to methods and systems for managing power consumption of computer memory systems.
2. Description of the Related Art
Power consumption by computers and computing devices is an issue for many reasons. Examples include portable computing devices that have a limited power source (i.e., battery), large server computer systems that process large quantities of data but also consume large quantities of power in the process, and the cooling required to remove the heat that is produced as the power is consumed by the computing devices. The total power consumed by a computer is constantly being driven lower and lower. By way of example, a portable “laptop” computer's battery is a finite power source. One aspect of performance of a laptop computer is how long it can operate on the battery. A larger and heavier battery can typically extend the operating time but because the laptop is also rated for its light weight, increases in battery weight are typically avoided. Therefore the power management and efficiency of a laptop computer is an important feature.
Another example of power management is in a server computer. A server computer processes so much data that it also consumes large quantities of power. Further, when multiple servers are combined into a “server farm” to work together, the power consumption becomes very high. Because much of the consumed power is converted to heat, the servers are typically actively cooled by air conditioning and refrigeration systems which further increases the overall power consumption of the server.
Power efficiency of computers has been addressed through various methods such that now the power consumption of a high efficiency computer's memory system can far outweigh the power consumption of the processor itself. By way of example, a high efficiency processor consumes approximately 40 watts of power. Such high efficiency processors in a server can have 16 or more DRAM (dynamic random access memory) DIMMs (dual in-line memory modules) in the memory system. Each of the DIMMs consume approximately 14 watts of power at maximum access (i.e., read/store) rates, resulting in a total of 224 watts power consumption for the 16 DIMMs, at maximum access rates.
Typical power usage, though, is much lower. The reason typical power usage is lower is because the DIMMs are not always being used at maximum access rates. Each time a memory cell within a DIMM is written to or read from, a small amount of power is consumed. Therefore, the number of times a DIMM is accessed in a given time interval impacts the total power usage of that DIMM.
FIG. 1 is a high-level block diagram of a typical computer system 100. As shown, the computer system 100 includes a processor 102, ROM 104, and RAM 106, each connected to a bus system 108. The bus system 108 may include one or more buses connected to each other through various bridges, controllers and/or adapters, such as are well known in the art. For example, the bus system 108 may include a “system bus” that is connected through an adapter to one or more expansion buses, such as a Peripheral Component Interconnect (PCI) bus. Also coupled to the bus system 108 are a mass storage device 110, a network interface 112, and a number (N) of input/output (I/O) devices 116-1 through 116-N.
The I/O devices 116-1 through 116-N may include, for example, a keyboard, a pointing device, a display device and/or other conventional I/O devices. The mass storage device 110 may include one or more of any devices that are suitable for storing large volumes of data, such as a magnetic disk or tape, magneto-optical (MO) storage device, or any of various types of Digital Versatile Disk (DVD) or Compact Disk (CD) based storage.
Network interface 112 provides data communication between the computer system and other computer systems on a network such as a local area network, wide area network, the Internet or other networks. Hence, network interface 112 may be any device suitable for or enabling the computer system 100 to communicate data with a remote processing system over a data communication link, such as a conventional telephone modem, an Integrated Services Digital Network (ISDN) adapter, a Digital Subscriber Line (DSL) adapter, a cable modem, a satellite transceiver, an Ethernet adapter, or the like.
The RAM 106 can include multiple DIMMs 106-1 through 106-N. In a typical application, a average access rate of a DIMM results in an average 6-watt power consumption. However, as discussed above, the maximum access rate can cause the power to increase to as much as 14 watts for each DIMM 106-1 through 106-N.
In view of the foregoing, what is needed is a system and method to reduce or limit the maximum power consumption of each DIMM as seen by the power supply without significantly impacting the performance of the processor.